JamesC

iTrader: (5)

Is there supposed to be one or two in place?

JamesC

Damon

One.

I'm guessing you found two and are scratching your head over this?

JamesC

iTrader: (5)

Yep. Found it a few minutes ago. What's up with two? Mistake?

BTW, when I turned the idle mixtures screws back in, I found, to my surprise, that they not symmetrical from side to side. Is that common?

JamesC

paulo57509

I think some Holleys come with a front and rear power valve.

JamesC

iTrader: (5)

Talking single valve which had two gaskets.

JamesC

five7kid

iTrader: (14)

They were generous and gave you a spare.

sofakingdom

iTrader: (1)

There are 2 different power valve styles, and a gasket that goes with each. Just use the one that works with whichever power valve style you end up with.

If memory serves, if you have the PV type with the 2 big rectangular windows, it uses the simple round gasket (this is the more common these days); if you have the type with a bunch of drilled-looking holes, it uses the one with the little tabs toward the inside.

skinny z

And as for your idle mixture screws, they should be evenly adjusted.

DonW

I almost did the same thing when changing out the PV the last time. The gasket stuck to the carb and I slid the new gasket on the new PV and screwed it in. Im not sure it would have caused any issues, but I caught it when I went looking for it to store in the same baggy with the old PV....woulda had two on there lol.

Idle mixture screws being off more than 1/8th of a turn difference from one another might cause some issues. I used a black sharpie and made 8 tiny dots around the screw and one on the screw itself to ensure I was turning them the same amount each time.

sofakingdom

iTrader: (1)

What I do w idle mixture screws, is turn them to wherever they seem to want to be, then turn the motor off, turn them all the way in counting the turns, then back them both back out to the average plus about ¼ turn. Repeat if necessary. If they absolutely REFUSE to become ideal at less than 1/8 turn different or so, I begin investigative surgery.

DonW

the dots are an easy trick i learned from someone else. You just start off making the first 4 North, South, East, West. Then fill in another dot between each mark. Works like a charm.

DonW

Sofa, your way confuses me a little. Tell me if I did it wrong.
With the vacuum gauge hooked up and screws turned all the way in and then backed out 1 and a half turns. Start the engine and proceed to back them out or turn them in the exact same amount turn for turn until the highest vacuum is reached. THEN I have my son put the car in drive and just lightly depress the accelerator while stepping on the brake to put it under a load. While its under a load I adjust them again the exact same amount until I have the highest vacuum reading.

This method worked well for me...

sofakingdom

iTrader: (1)

Not wrong; each technique you use, might produce different results, but 2 things are important: (1) does it produce the results that matter TO YOU? i.e., some of us might care more, or less, about max power, best throttle response, best gas mileage, and so on; does the method you use give YOU what YOU want? and (2) can you RELIABLY REPRODUCE it?

The "highest vacuum reading" is a real good way to find where the engine likes it. Vacuum = how fast the engine will run, at that throttle opening and under those conditions (load, mixture, RPM, spark timing, etc.); so it's a very sensitive indicator of the engine's "happiness".

"Best" idle almost always corresponds closely to highest idle vacuum.

My methodology doesn't depend on instruments (e.g. vacuum gauge), it's intended for strictly "by ear" tuning. Instrument things like vac gauge, O2 sensor readings, etc. help by giving more detailed information.

Edwardgp

Agree, highest vacuum reading is a great way to set idle screws.

DonW

Something tells me you have been doing it long enough to do in your sleep! Not me, I would have been lost without the $25 vacuum gauge lol

I even used it to time the distributer. Although, I did learn that a higher vacuum is obtainable but not nescessarily the best. I first got the highest vacuum reading but it pinged under WOT. Then I just backed it off a little (retarded). Then I used the vac gauge again on the idle mix screws as mentioned above to get the highest reading. That along with your tuning sticky and an adjustable secondary really made it get up and go and get great mileage while doing it. Ive been so happy with it that I havent been in a hurry to put in the 350 yet.

Damon

DON'T be shooting for "max idle speed" with your ignition timing. That WON'T work.

For setting idle mixture screws, though, it works just fine.

DonW

Sorry Damon...not sure what you mean by "WONT WORK"
Setting your ignition timing with a vacuum gauge is an excellent way if you know what you're doing. A vacuum gauge used in conjunction with a timing light and a "good ear" was THE ONLY WAY just a few short years ago

Heres a good article ...

http://classicinlines.com/vacuum.asp

Damon

By "won't work" I mean it WON'T WORK. Sure, it'll idle like a champ if all you ever want to do is idle your engine under no load.

Setting timing for "highest idle speed" will be somewhere between slightly and massively over-advanced when the engine is under load.

Straight from that article, they even make note of this (emphasis mine):

"with the engine still at idle, advance or retard the ignition until the highest steady vacuum reading is obtained. Then retard the timing until the vacuum gauge reading drops slightly, approximately one half to one inch. In some cases, you may need to retard the timing up to two inches to prevent pre-igniton (pinging). "

DonW

I see. Not sure how I missed what you were saying. Setting it for max vacuum won't work. I never said do that, but using a vacuum gauge in and of itself is a great tool. Like I said above, I found max vac and then backed mine off a little until pinging stopped. THATS HOW IT WORKS. then moved on to the carb and obtained max vac again with the gauge. It's a great tool. I took it as you were saying that a vacuum gauge won't work for setting ignition timing. It works just fine as long as you know to back off 1-2 degrees

skinny z

A vacuum gauge is also a great tool to have on board all the time. You can learn a lot about how your engine is performing with one of those mounted in the dash. It's absolutely indispensable when carb tuning.

five7kid

iTrader: (14)

I don't know how old your carb is, but Holley didn't have the best reputation for cast & machining quality 10-15 years ago. The last one I bought had terrible inconsistencies in the circuits. I could never get the stupid thing to idle until I discovered one secondary transition slot didn't even go down to the butterfly until well open. Their metering block castings were also notorious for being porous. By the time I got done with that carb, the only things I hadn't replaced were the fuel bowls. They seem to be doing a much better job these days.